Morphometric analysis of the sural nerve in experimental dorsal rhizotomy in rats.

To investigate the histological changes in the sural nerve by the damage to the centrally projected axon (CPA), we examined light-microscopic findings after dorsal rhizotomy. The L4-6 dorsal roots were cut unilaterally near the entry zone, with minimal laminectomy, in 27 anesthetized 8- to 10-week-old Sprague-Dawley rats. Animals were killed 1, 2, 4 and 8 weeks and 6 months after surgery, and morphometric results from the sural nerves on the side of the rhizotomy were compared with those from the unaffected side. There were no significant differences in total number, density, frequency distribution of diameters, thickness of myelin, and axonal circularity of myelinated fibers. In an analysis of teased fibers, neither demyelinated nor remyelinated fibers were found, and significant axonal degeneration was found in only 1 of 27 sural nerves on the side of the rhizotomy. These results suggest that pathological damage to the sural nerve is not the product of CPA lesions, even if the subject has dorsal root lesions at some distance from the ganglion.